Controlling unauthorized immigration along the U.S.-Mexican border has become an increasingly important national objective. Despite initial bipartisan support for this strategy, concerns about its effectiveness are beginning to emerge. This report addresses the following questions: Has increased border enforcement changed decisions to migrate? Has it changed where and how people cross the U.S.-Mexican border? Has it led to an increase in migrant deaths? Has it altered how long immigrants stay once they arrive? Has it reduced the total number of unauthorized immigrants living in the U.S.? What other policy options might help curb unauthorized immigration?